Luftwaffe responses.  
  Part 4.  
  General J. Kammhuber in front of the GefStd of NJG 1 at Deelen.  
  The Bomber Stream as depicted in part 3, was becoming increasingly difficult to detect with radar.  It must be recalled, that at this point the Luftnachrichten Dienst did not use scanning radars with a PPI display.  The search radars were slewed manually and when the sky was filled with chaff there were thousands of echoes to chose between.  PPI radars were in the process of being introduced as a matter of priority, but it would not be until the end of 1944 they were in widespread use and then mainly only at the Stellung 1'ordnung.  However if the Bomber Steam was fairly well hidden from radar it still stood out as a Christmas tree on a clear winter night:  
  a.   The first reaction when one is jammed is to change frequency.  At this time the German radars worked on a fairly narrow frequency band (about 10 Mhz wide) so this measure had very little effect and most air warning radars worked on a frequency around 125 Mhz (+/- 25 Mhz).  The two next measures are a bit more time consuming to implement: Frequency diversity and frequency agility.   
  Frequency diversity entails the deployment of several types of radars working on a wide range of frequencies.  This measure was widely employed by the Wehrmacht.  At the end of the war the Luftwaffe had search radars with frequencies spread from 34 to 240 Mhz.  This complicates the jamming challenge tremendously, and Chaff has to be cut in many different lengths in order to be effective.  
  Frequency agility entails that it is possible to change the frequency over a fairly wide band hopefully to a frequency less affected by jamming.  German radars produced late in the war were equipped with "Wismar", which provided for change of frequency over up to 100 Mhz further complicating the jamming  and Chaff employment problem for the adversary.  Chaff, which effect a frequency around 30 Mhz, needs to be about 5 m long!  This was produced and employed by the allies under the name Rope - for good reasons.  Weight and bulk quickly becomes a limiting factor.  
  And finally scanning radars (Dreh Freya, Freya Verbunkert and Jagdschloss) with a PPI were developed and deployed.  On a PPI display the operator can observe a 2D air situation through 360 degrees, multiple tracks can be observed at the same time and it is possible to track Chaff corridors.  
  b.  The jamming could be and was triangulated.  Albeit it might be difficult from the ground to single out specific jammers, the track and progress of the Stream could still be followed.  
  c.  In order to navigate accurately, find and mark the target, the Stream was lead by a number of Pathfinders.  Further Pathfinders were spaced within the stream.  The Pathfinders were bombers with an experienced crew in bombers equipped with the H2S ground mapping radar.  Their task was to lead the stream, drop route markers (parachute flares) at turning points and mark the target with ground or sky markers.  The H2S could be tracked with passive radar receivers (FuMB 11/15 Korfu 812/274) and a triangulation was again possible.  
  d.  The bombers were equipped with a tail warning radar (Monica), this could be detected and tracked as described above utilizing the FuMB 4 Samos.  
  e.  And finally the bombers were equipped with IFF.  This piece of equipment was intended to identify the bombers electronically for the RAF Control & Reporting System, and of course it should be switched off when approaching enemy air space.  But some crews simply forgot.  Further there was a widespread belief amongst bomber crews, that their IFF had a jamming effect against the Würzburg-Riese, so some crews left it on on purpose.  The Luftwaffe developed and deployed the Freya Flamme, which could interrogate the allied IFF, thus in one stroke giving range bearing and identification of RAF bombers despite all the jamming effort.  These radars were again deployed at the Stellung 1'ordnung.  

A special organization was established in order to, through passive receivers, detect, track and exploit emissions from the bombers: The Funkmess Aufklärungs Dienst.  Stations from this organization were deployed through Germany and the occupied countries from the spring 1944 and onwards.  Reports from these stations were passed to a Meldekopf/Gefechtsauswertung where it was processed and then passed to the GefStd of the JD and displayed on the Hauptlage Karte along with the radar plots. In Diogenes the nickname HUGO was used to describe the Funk.Auf.Kl. Cell.  If this was a site specific or a generic name is unknown.

  German night fighters were equipped with receivers so they could home on Monica and H2S receivers (Flensburg and Naxos).  Jamming homers (Freya Halbe) were also installed in a number of German night fighters, but for some reason the use of this system never became wide spread.  
  In the JD it was thus possible to establish the track of the Bomber Stream, possibly identify the point and through the employment of Zahme Sau infiltrate night fighters into the stream.  The night fighters were greatly aided by their passive devices to find the stream and to single out Pathfinders for attack.  


A Bf 110G-4b/R3 equipped with FuG 202 and SN-2.  Window affecting one of the radars would not affect the other.  This ensured a certain degree of immunity from interference.

  With the establishment of the Funk Aufklärungs Dienst, it was easier for the JD to distinguish between decoys and the real Stream.  The diversion raids usually had few or no H2S equipped aircraft in their composition and consequently they were ignored.  
  With the employment of Chaff, Himmelbett-Verfahren had for all intent and purpose ceased to be effective except against single aircraft, which for some reason were outside the Stream and thus could not benefit from the Chaff.  Y-Verfahren was greatly complicated through the radio jamming.  The German response was twofold.  In stead of attempting to give Y-Control to each individual night fighter the entire Haupt- or Reichlage was broadcast on a frequency band not affected by the jamming (3 - 6 Mhz).  This gave the night fighter crews the track of the stream. The night fighters were expected to navigate autonomously utilizing the Schweres Funk Feuer (Radio Beacons) established throughout the area of responsibility.  Many of these beacons had been established before the war to serve civilian air traffic and the Luftwaffe alike.  A radio beacon will just give the crew a bearing on the radio compass, and the crew had to take bearings from at least two beacons in order to get a fix.  The position thus obtained is not very accurate, but it would give the night fighter crew a pretty good idea about what course to fly, in order to intercept some part of the Stream.  This CONOPS was called Ungeführte Zahme Sau.  Both types of Zahme Sau were at the end of 1944 re-named Verfolgungs Nachtjagd.  
  The Haupt- or Reichlage was broadcast in the same, very simple format as later used in the system described below.  This could easily be transmitted as voice, morse of data.  
  In addition the Bernhard/Bernadine was introduced.  This system provided for the transmission and reception of key information about The Stream and the bearing from the transmitter.  


Schweres Funk Feuer autumn 1944.



Schweres Funk Feuer 14 at Rønne.  (Author's collection via Bornholms Museum).


The Beacon Bible.

  As RAF Intelligence got a deeper understanding of Wilde and Zahme Sau, it was realized that it was of importance to collect detailed information on the beacons (Funkfeuer) used by the Luftwaffe.  Part of the tactic employed during Zahme Sau was to order the nightfighters to fly to/orbit specific beacons in anticipation of the passing of The Bomber Stream.  So by monitoring the broadcast frequencies and with the knowledge of the location of the beacons it was possible to assess the accuracy of the German plotting, the effect of the jamming and decoy effort and to order RAF intruders to the appropriate beacons.  The result of the aforementioned intelligence effort was a document called The Beacon Bible.  After the war it was filed as PRO AIR 40/1343.  During his research Mr. Michael Grube of came across the document and filled a spread-sheet with the information.  Mike has now decided to make this available to all of us, and I am grateful for his permission the make this public on GYGES.  

The Beacon Bible.

  Luftwaffe response to allied utilization of navigational aids.  
  3 systems were used by the allies to facilitate navigation, marking and precision bombing: GEE, Oboe and H2S.  GEE was jammed by the Heinrich jammer, Oboe by Anti-Bumerang and H2S by Roderich.  
   In the night fighter the signal was recieved by the FuG 10P equipped with the PeilG 6 and bearing displayed on the Funkpeiltochterkompass PKT/p2.  



The Bordfunker position in a Bf 110G-4, please note the PKT/p2 in the lower right.


 The PKT/p2.